Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
  • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
  • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
  • G01T1/16—Measuring radiation intensity
  • G01T1/20—Measuring radiation intensity with scintillation detectors
  • G01T1/201—Measuring radiation intensity with scintillation detectors using scintillating fibres
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
  • G01T3/00—Measuring neutron radiation
  • G01T3/06—Measuring neutron radiation with scintillation detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
  • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
  • G01N23/06—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption
  • G01N23/09—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and measuring the absorption the radiation being neutrons

Definitions

• This invention pertains to the detection of contraband and particularly to the
• X-ray systems are sensitive to differences in X-ray absorption coefficients in
• CT X-ray computed tomography
• TAA Thermal neutron absorption
• TNA in nitrogen, TNA has an unacceptably high false alarm rate.
• TNA include that the neutrons must be thermalized, the n, ⁇ cross section is in the
• Pulsed fast neutron absorption detects the inelastic scattered gamma
• Grenier discloses a system based upon the n, ⁇ reaction with pulsed 14 MeV neutrons. Grenier (US 4,882,121). Grenier's system uses the inelastic scattering cross
• Grenier's system is based upon secondary interactions (detecting gamma rays resulting from first order interactions),
• neutrons correspondmg to the characteristic neutron resonances of carbon (C), nitrogen
• the resonance absorption cross sections are in the
• neutron beams simultaneously from one machine may reduce this impediment in the future.
• single scan system relates to the neutron probe.
• the methods outlined by Overley and the Guidelines use one or more collimated neutron beams.
• a single beam, single scan system requires an uncollimated beam which expands in a cone shape, so that a sample object can be placed at the arc at the end of the cone for coverage by the
• a single beam, single scan system should use a neutron beam with an angular distribution of neutrons relatively flat around 0 degrees. This flat angular
• a workable detection system would require numerous detectors with a relatively small spatial resolution. For example, a 4 cm by 4 cm spatial resolution is generally required in order to locate lethal amounts of explosives. To cover a 60 cm by 80 cm suitcase, a system would require approximately 300 detectors. In general, the detector array would be even larger to cover larger containers or to cover containers
• thermal detectors could not be used in a fast neutron attenuation system.
• thermal energy detectors could not be used in a fast neutron attenuation system.
• neutron detectors cannot be used to detect fast neutrons due to the lower detection
• a variation includes a neutron camera, which also must be used
• detectors are not configured for time of flight measurements.
• X-y detectors for fast neutrons do exist, but cannot be used for time of flight
• neutron attenuation measurements One type is the multi-wire proportional counter
• MWPC consists of thin gas filled cells with small wires running parallel through the cells.
• the wires are placed at high voltage and when a proton enters the cell close to a particular wire, a voltage pulse is created. By recording the position of the voltage
• the position of the event is known in the direction perpendicular to the wires.
• De Volpi discloses a method for high-resolution radiography by using gamma
• De Volpi measures changes in the density of sample materials and is not workable in a neutron attenuation system using time of flight measurement. Also, De Volpi uses nuclear reactors as his source of neutrons and so the neutrons are in the KeV energy range or lower. Although De Volpi does not mention the type of neutron detector, detectors
• KeV energy neutrons and lower energies generally are not useful for detecting
• Attenuation system must be capable of nanosecond timing resolution. There is no
• Another class of x-y fast neutron detectors uses a number of photomultiplier tubes placed behind a scintillator. Strauss (US 4,454,424). When neutrons are incident on the scintillator, some of the neutrons are absorbed and cause scintillations via fission. The recoil fission fragments create pulses of light which are detected by the
• the x-y position of the neutron interaction is determined by the particular photomultiplier tube which senses the light pulse.
• the Strauss detector does not measure neutron energy.
• the Strauss detector does not measure neutron energy.
• Gomberg discloses an explosive detection system based only on elastic
• Gomberg (US 4,864,142). Gomberg describes a low count
• neutron source must be varied from 0.1 to 4.2 MeV, which is a complicated procedure and cumbersome to implement.
• An airport system based on Gomberg's method could take hours to scan a single piece of luggage.
• Yet another advantage of the present invention is detection of hydrogen, which
• a contraband detection system produces a single, cone shaped, pulsed white neutron beam with a relatively flat neutron angular distribution around zero degrees.
• a sample is placed in the beam at a point at which the beam has expanded sufficiently
• contraband detection system determines substances concealed in a sample object (such as
• a processor configured to control the plurality of other elements, including nitrogen, oxygen and carbon.
• the contraband detection system measures the neutron attenuation spectra
• the contraband detection system includes a neutron point source for producing a pulsed beam of fast white neutrons in the shape of a cone with a relatively flat neutron distribution around 0 degrees; a spatial neutron ⁇ - ⁇ detection array (R- ⁇ - ⁇ with constant
• R which records fast neutrons at neutron energies from approximately 0.5 MeV to beyond 15 MeV; means for situating a sample object between the source and the detection array; a spectra analysis system for determining the neutron attenuation
• the neutron point source produces pulsed fast white neutrons having a sufficient energy range whereby removal of neutrons from the beam (by absorption or scattering) caused by a plurality of contraband-indicating elements is used to deteimine the neutron attenuation spectra of a sample object.
• the ⁇ - ⁇ detector array comprises an array of neutron detector elements
• Each of the detector elements is aligned along a neutron path with a corresponding three-dimensional sector of the sample object
• the surface of the detector array is in the
• Fig. 1 is a schematic view of a detection system according to an embodiment of the invention.
• Fig. 2 is an isometric view of the R- ⁇ - ⁇ (with constant R) detector of Fig. 1.
• Fig. 3 shows a schematic of the electronics.
• Fig. 4 is a graph showing total neutron cross section curves for hydrogen,
• Fig. 5 is a graph showing the neutron attenuation of an average suitcase, a 4 cm
• Fig. 6 shows a linear regression theory fit to the measured C-4 neutron attenuation curve of
• Fig. 1 shows a contraband detection system 18 including a neutron source 20; a
• neutron detector assembly 22 a neutron detector assembly 22; a spectra analysis system 24; and, a classification
• FIG. 1 also shows a conveying system 28 for introducing a sample object
• the neutron source 20 includes an accelerator 30 for generating a pulsed
• deuteron beam 32 for directing the pulsed deuteron beam to a target 34.
• the pulses of the deuteron beam 32 have a
• the neutron source 20 is enclosed in
• shielding 38 which is in the shape of a sphere or the like with an aperture oriented so
• the accelerator 30 is a small tandem accelerator with a terminal voltage of between 2.0 MeV and 2.5 MeV
• the accelerator utilizes a negative ion source at ground potential and accelerates the negative ions to the energy of 2.0
• the target 34 has a composition such that impingement of the pulsed deuteron
• neutron beam means a beam of neutrons having energies in a range from
• the beam has a relatively flat neutron
• the neutron detector array 40 is placed about three to
• detector array 40 is comprised of an ⁇ - ⁇ array 40 of neutron detector assemblies 22.
• the detector array 40 includes enough detectors to cover a large suitcase with a spatial
• the particular detector array 40 shown in Fig. 2 includes twenty-five columns of
• detector elements 42 with each column consisting of twenty-five detector elements 42.
• array 40 may take on other sizes in accordance with
• FIG. 3 shows a schematic diagram for the electronics.
• the neutron detector assembly 22 is comprised of a neutron detector element
• the photomultiplier tubes 44 are arranged in a photomultiplier tube 42, a photomultiplier tube 44, and a voltage divider 46.
• the photomultiplier tubes 44 are arranged in a photomultiplier tube 42, a photomultiplier tube 44, and a voltage divider 46.
• each voltage divider 46 has less than a nanosecond rise time and each voltage divider 46 is connected through
• the spectra analysis system 24 includes a deuteron beam pick-off 50; a time pick-off controller 52; an amplifier 54; an array 56 of time-to-amplitude converters
• TACs pulse shape discrimination circuits
• the neutron detector assembly 22 can acquire configurations other than that
• shape discrimination circuit 60 can be replaced with scintillation and detection
• the deuteron beam pick-off 50 is a cylinder which senses when a charged
• deuteron pulse travels through the cylinder.
• pick-off 50 is amplified by the amplifier 54 and is sensed by the time pick-off 52.
• stop pulse which is applied to each of a plurality of converters in the array 56 of time-
• Each of the time-to-amplitude converters included in the array 56 is associated
• Each of the TAC units in array 56 is connected to receive a real time "start" pulse from the neutron detector assembly 22.
• each TAC in array 56 receives a real time stop pulse from the time
• signals from the detector elements 42 can use signals from the detector elements 42 as a stop signal and signals from the time pick-off as the start signal as is well known in the prior art.
• the pulse shape discrimination circuit 60 includes a number of pulse shape is discrimination circuits corresponding to the number of detector elements 42 included in
• the pulse shape discrimination circuits in network 60 discriminate gamma
• the multi-channel analyzer array 58 includes a multi-channel analyzer (MCA)
• Each MCA in array 58 is connected to receive the output
• the associated MCA in array 58 sorts the amplitude pulses from the activated TAC to give a time of flight spectrum for the activated TAC.
• the amplitude pulses are then categorized into channels, with each channel
• array 58 generates outputs which are indicative of the number of counts for each
• the processor 26 is a conventional data processing system having a central processing unit, memory, an arithmetic logic unit, and an input/output
• the processor 26 has its input/output interface/controller 62
• bus 64 to the MCAs included in array 58 to receive the data utilized to
• total neutron cross section is the total neutron cross section
• the input/output interface/controller 62 of the processor 26 is also connected to a printer
• the central processing unit of the processor 26 executes instructions for evaluating the neutron attenuation spectra for the plurality of contraband-indicating
• each MCA in array 58 is connected to
• the processor 26 performs calculations for each of the MCAs included in the MCA
• detector elements 42 included in the array 40 The types of calculations performed by the processor 26 with respect to the data obtained from each of the MCAs included in
• array 58 for generating the spectra is in accordance with standard techniques such as
• the processor 26 creates neutron attenuation spectra for each neutron
• neutron attenuation spectra for each detector element 42 is stored in memory and also
• depiction is selectively displayable both on the CRT display screen 68 and on hardcopy
• a suitable scintillator is a liquid
• photomultiplier tubes 44 can be any suitable commercially available tubes, such as
• voltage divider 46 is manufactured by ORTEC as model 261.
• the contraband detection system 18 of the present invention detects the
• contraband-indicative elements including nitrogen, hydrogen,
• system 18 of the present invention is optimum if several peaks or distinguishing
• Fig. 4 is a graphic depiction of the superimposed total neutron cross section
• peaks shown in Fig. 4 correspond to neutron energies at which neutrons are
• carbon has one large neutron removal peak at 2.07 MeV and a smaller neutron
• Oxygen has a large doublet at 1.69 MeV and 1.65 MeV.
• Nitrogen has two prominent peaks, one on each side of the large oxygen doublet: 1.78
• the central processing unit of the processor 26 includes instructions, which,
• the processor 42 locates elements in sample object 29 for which the processor 26 makes a contraband classification determination, the processor outputs a signal to the alarm device 70.
• the contraband detection system 18 of the present invention analyzes the neutron attenuation spectra for three elements (C, N, and O) which have neutron-removal peaks in the range of fast neutron energies, and a further element (H) which does not have a neutron-removal peak in the range of fast neutron
• the processor 26 can utilize software including regression theory to determine
• processor 26 as independent variables. For each detector element 42, values of In (N-/N), with the N values having been obtained from the associated MCA in array 58, are supplied to the processor 26 as dependent variables. The processor 26 then outputs,
• contraband-indicating element as well as the standard error for each of the contraband
• the total cross sections used as the independent variable can be obtained from
• FIG. 4 shows a graph of the total cross sections of H, C,
• Fig. 5 shows a graph of the measured neutron attenuation of an "average"
• Fig. 6 shows a regression theory fit to the C-4 attenuation curve of Fig. 5.
• the resultant numbers can be evaluated using atomic ratio expressions
• processor 26 can determine whether the suitcase contains polyurethane and other similar
• plastics can also determine the type ofexplosive or plastic in the suitcase.
• the processor 26 determines that any detector element 42 has detected contraband in
• the processor 26 activates the

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• 1995
  • 1995-01-31 US US08/380,953 patent/US5606167A/en not_active Expired - Lifetime
• 1996
  • 1996-01-31 EP EP96903792A patent/EP0811157A4/de not_active Withdrawn
  • 1996-01-31 WO PCT/US1996/001633 patent/WO1996024048A1/en active Application Filing
• 1997
  • 1997-02-21 US US08/803,893 patent/US5880469A/en not_active Expired - Lifetime

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